1. Field
This disclosure relates to photoelectric conversion elements and, in particular, to a photosensitized photoelectric conversion element. The term, photosensitized photoelectric conversion element, is used also to refer to dye-sensitized solar cells and dye-sensitized power-generating elements capable of generating power in an environment, such as an indoor environment, with a relatively low illuminance.
2. Description of the Related Art
In recent years, dye-sensitized solar cells known as Gratzel cells have attracted much attention as new photoelectric conversion elements (refer to Japanese Patent No. 2664194). A Gratzel cell is constituted by a photoanode, a counter electrode, and an electrolyte medium disposed between the photoanode and the counter electrode. A photoanode typically includes a conductive layer that transmits visible light and a semiconductor layer containing a photosensitizer and formed on the conductive layer. The semiconductor layer contains, for example, porous titanium oxide. A dye serving as a photosensitizer is supported on a surface of porous titanium oxide. The dye is, for example, a ruthenium (Ru) complex. The counter electrode is, for example, a platinum electrode. The electrolyte medium is, for example, an electrolyte solution containing an oxidation-reduction substance (mediator).
Various studies have been conducted on improvements of properties of Grätzel cells. One of the studies involves search for a dye that can improve photoelectric conversion efficiency (hereinafter simply referred to as “conversion efficiency”). Ru complexes, merocyanine (for example, refer to Japanese Unexamined Patent Application Publication No. 2004-115636 (Japanese Patent No. 4080288)), and various other dyes (refer to Japanese Unexamined Patent Application Publication No. 2004-200068 and International Publication No. 2012/121192) have been investigated so far.
However, sufficiently high conversion efficiency has not been achieved with existing dyes. In particular, photoelectric conversion elements that exhibit high conversion efficiency even in an environment, such as an indoor environment, with a relatively low illuminance are highly anticipated.